Resolving Expect ... Not found in the archives.
While a more fuzzy search disregarding letter case and accepting
substrings was done, we are sorry to say that it yielded no possible
candidates for installation either.
Questions to consider:
Have you spelled the name correctly ?
Including the proper case of characters ?
Note that teacup's 'search' command allows you to locate packages by
subject, categories, and the like.
Aborting installation, was not able to locate the requested
entity.

Pansion suggested that the Expect package is 32-bit and won't work with 64-bit Tcl -- I had the same problem and after downloading the 32-bit version, teacup search Expect showed a win32-ix86 Expect package. Then teacup install Expect installed the package correctly.

You can also try installing an older version of Tcl - 4.6.20.0 32-bit has Expect included in the Tcl install.